JP2918385B2 - Surface treatment method for stainless steel members - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel member used as a component of an ultra-high vacuum application device such as an electronic device thin film production / surface analysis device, a bio / pharmaceutical raw material production, and an ultrapure water production device such as a substitute for cleaning of CFC. Stainless steel with excellent gas release, ion elution, smoothness and cleanliness required to achieve high quality products, high precision measurement, aseptic process, and detoxification of waste The present invention relates to a method for surface treatment of a steel member.

[0002]

2. Description of the Related Art In recent years, in the electronic equipment industry, high integration and high performance of electronic components have been progressing, and ultra-large scale LSIs having a minimum processing dimension of submicron order have been manufactured. Of course, the raw material supply system, that is, production of gas and pure water, storage containers, fine particles mixed from systems such as piping and its members, gaseous impurities released from the member surface, ionic impurities eluted, Propagation of bacteria and the like makes the production space imperfect. Such contamination causes crystal defects of semiconductors, poor film quality of thin films, poor uniformity of film-forming etching, pattern defects, etc., leading to a reduction in product yield and a reduction in processing speed, which adversely affects productivity. As the integration and performance of LSIs increase, securing a clean space is becoming more serious.

[0003] Therefore, it is necessary that raw materials and pure water used in the production stage of electronic equipment and semiconductors are also of ultra-high purity, and strict regulations are imposed on the quality of piping members for producing and transferring these. For example, a product having high cleanliness and smoothness is desired for the inner surface of a tube.

[0004] From such a viewpoint, a weldable metal material is used for a vacuum vessel, a gas pipe, and the like, and among them, stainless steel, which has better heat resistance, corrosion resistance, and gas release properties than other materials, is widely used. I have.

[0005] Ultra-high vacuum by reducing the amount of gas released from the vacuum vessel and vacuum system means lowering the density of gas and dust particles in the space, which increases the range up to collision of spatially moving molecules. , Preventing unnecessary scattering. In addition, since the amount of particles or the like incident on the unit surface is reduced, the time required for the clean surface to be contaminated with impurities is lengthened, and a good surface with high purity can be secured accordingly.

By the way, in the case of a film forming process using a vacuum, it is necessary to exhaust unnecessary gas in the system including the vacuum chamber before the film forming operation. The introduced process gas is contaminated and a high-quality thin film cannot be produced. Also, if the space is not sufficiently clean, the surface of the substrate remains contaminated, and there is a problem that the film formation interface becomes defective. Therefore, when fine processing is required, the initial conditions of the process are clean. In addition, high vacuum is required.

On the other hand, in ultrapure water pipes and the like, organic materials such as vinyl chloride resin having excellent corrosion resistance to pure water have been used. However, even with such a material, there is a drawback that a trace elution of organic components (additives such as residual monomers and plasticizers) from the main body and the joint cannot be completely prevented. Furthermore, recently, high-temperature cleaning with pure water has been attracting attention in connection with environmental problems, and organic materials have a problem with heat resistance.
In addition to the softening, there is a problem that the amount of eluted organic components is greatly increased. For this reason, attention has been focused on weldable metal materials as constituent materials, and in particular, stainless steel materials having better heat resistance and corrosion resistance than other materials have come to attract attention.

[0008] By the way, from the viewpoint of suppressing adhesion, release and elution of impurity components, surface treatments such as bright annealing, cold working, electrolytic polishing, and the like are performed on the constituent materials for the purpose of smoothing and cleaning the surface. Has been adopted. However, if the surface of the constituent material is subjected to mechanical processing, if the deteriorated layer remains, impurities may be adsorbed and released, impairing the vacuum environment and the cleanliness of gas and pure water. There is also. For this reason, when stainless steel is used as a constituent member, a surface processing method has been adopted which also has a smoothness at the same time as removing a deteriorated layer formed during the manufacturing process.

[0009]

However, even in the case of stainless steel which has been subjected to conventional surface processing such as electrolytic polishing, gas components dissolved during refining, adsorption and occlusion during surface processing and storage. Dust and gas may be released into the space. In particular, in the method of electrolytic polishing in water, the atomic gas components accompanying the electrolysis are dissolved and occluded in the metal, and the moisture is taken in the passivation film of stainless steel formed in water, so that it can be used later. In such a case, there is a problem that the release of moisture continues forever, an ultra-high vacuum cannot be achieved, and the clean process gas is contaminated with moisture.

For example, heavy metal ions such as Fe, Cr, and Ni, which are constituent elements of stainless steel, may be eluted in pure water. Therefore, in order to reduce the gas release property and the ion elution property of the electrolytically polished stainless steel, a method of performing an oxidation treatment in various atmospheres as a post-process has been proposed. This method solves the problem of the surface caused by electrolytic polishing by providing a surface oxide film having an appropriate thickness and a crystal structure.

For example, there is a method in which electrolytically polished stainless steel is heated and oxidized at 280 ° C. to 580 ° C. in an atmosphere having an oxygen content of 25% by volume or more (JP-A-64-31956). It cannot be applied to a device that has a high oxidation temperature and contains a non-heat-resistant material such as a low-melting-point material and packing, and also causes a problem of distortion of components due to temperature. SUS304 or SUS316 stainless steel, which is excellent in availability and price, is 50
When the material is heated at about 0 ° C. for a long time, chromium carbides are protruded from the crystal grain boundaries, and a phenomenon is liable to be caused to cause intergranular corrosion. Therefore, in order to avoid this problem, it is necessary to use a steel type which is less likely to cause intergranular corrosion, and it is inevitably expensive. Further, a method of forming an amorphous oxide film having a thickness (7.5 nm) or more by heating (Japanese Patent Application Laid-Open No. 64-87760).
However, this method utilizes an amorphous structure peculiar to electropolishing, and is limited to electropolishing, and has problems in controlling an unstable crystal structure and its thickness. Also,
The method of limiting the moisture content of the oxidizing atmosphere (dew point -10 ° C or less) and defining the thickness and composition of the oxide film (Japanese Patent Laid-Open No. 1-198463) recommends that the oxidation temperature be in the range of 300 to 550 ° C. And the high temperature is a problem.

The present invention has been made to solve the above-mentioned technical problems, and its object is to provide a gas release,
An object of the present invention is to provide a surface treatment method for a stainless steel member which is excellent in ion elution property, smoothness, and cleanliness and is used as a component of an ultra-high vacuum applied device and an ultrapure water production device.

[0013]

Means for Solving the Problems To solve the above problems, a method for surface treating a stainless steel member of the present invention comprises the steps of: polishing a stainless steel member polished to a surface roughness of 1 μm or less; 1 hour at 150-300 ° C in a dry oxygen atmosphere of 0.5-10% by volume.
This is a method of forming an oxide film on the surface of a stainless steel member by performing a heat oxidation treatment within a time range of more than 10 hours .

[0014]

According to the surface treatment method of the present invention, a dense oxide film is formed on the surface of a member at a low temperature by employing a treatment method having an action of oxidizing and removing impurities adhering to the surface of the member.

Generally, in an ultra-high vacuum apparatus, a vacuum pump oil,
There is a problem that the inner surface of the device may be soiled due to inadequate handling of the sealing member and handling, and there is a problem that a clean vacuum cannot be established without removing organic substances and carbon which are the main components of the soil. Removal of organic matter is indispensable because it leads to increase and propagation of bacteria.

Therefore, the strong oxidizing action of ozone, its generation is possible with a small apparatus, that is, it can be manufactured and supplied near the site of use, and there is no pollution in which only oxygen is a raw material and only oxygen remains after use. There is a characteristic that it is sex.

In the surface treatment method of the present invention, first, the surface roughness of a stainless steel member is polished by Rmax: 1 μm.
m or less. When the surface roughness exceeds Rmax: 1 μm, the specific surface area is increased, the surface is chemically active and impurities are trapped in the flaws, and the formed oxide film lacks denseness. Therefore, gas and surface elements on the inner surface of the member are easily eluted, and good characteristics cannot be obtained.

The formation of the oxide film is performed at 150 ° C. to 300 ° C. in a dry oxygen atmosphere having an ozone content of 0.5 to 10% by volume.
The heat treatment is performed in the above temperature range. As is clear from the examples described below, when the ozone content is less than 0.5% by volume, the ozone concentration is not sufficient, and it becomes difficult to form a good oxide film. When the heating temperature is less than 150 ° C., the temperature is reduced. It is too low to remove impurities such as moisture slowly, and it is difficult to form a good oxide film. By the way, when moisture is contained in the atmosphere, moisture remains on the surface and reacts with ozone to become corrosive, so that dry oxygen is required. In the case of dry air, the oxygen concentration is only about 20%, and it is not efficient to obtain the indicated high concentration of ozone using an ozone generator. The method of irradiating a low-pressure mercury lamp in oxygen is effective for removing organic impurities on the surface, but the ozone concentration is low and the concentration is insufficient for oxidizing metal. High ozone concentrations above 10% are not efficient with commercial ozone generators. If the heating time is less than 1 hour, the temperature distribution is not uniform due to the heat conductivity of the stainless steel, and a uniform oxide film cannot be formed, and the oxidation reaction is slow and a sufficiently thick oxide film cannot be obtained. On the other hand, when the heating temperature exceeds 300 ° C., ozone is self-decomposed, the oxidation effect of ozone is weakened, and the characteristics of low-temperature treatment are lost. In addition, the influence of thermal strain appears with the heat treatment. In addition, the oxidation time is 10
If the time is exceeded, excessive oxidation may occur, but mainly causes a problem in workability.

In the present invention, the other heating conditions described above are not particularly limited, but it is preferable that the heating conditions be such that a stable oxide film in which nickel and chromium are concentrated is formed completely and favorably.

Hereinafter, embodiments will be described. However, the present invention is not limited to the following embodiments, and can be appropriately modified. Further, the stainless steel according to the present invention substantially includes a Fe, Cr, and Ni component as a representative, and may be a stainless steel containing Mo, Ti, or the like.

[0021]

EXAMPLE A SUS316L stainless steel pipe (with a flange of both ends) having a pipe diameter of 20 A and a length of 2000 mm was subjected to buff polishing of various counts, and an electrolytic current density of 1 A / cm ² using a 20% NaNO ₃ aqueous solution. As a result of electrolytic combined polishing, a member surface having a roughness of 5 to 0.1 μm (Rmax) was obtained. Next, thermal oxidation treatment was performed under various conditions shown in the middle column of [Table 1] below. During the thermal oxidation treatment, test steel pipes were installed in a vertically split muffle furnace,
Atmospheric gases with various ozone contents were introduced into steel pipes from a high-purity oxygen cylinder of 99.9% or more (dew point -40 ° C or less) using a silent discharge ozone generator (high-frequency creeping discharge type ozonizer). Was completely replaced, and during the oxidation treatment, the gas flow rate was 1 l / min. The following tests were performed on these samples. (A) Test for measuring the amount of eluted metal Ultrapure water having a specific resistance of 18 MΩ · cm or more was sealed in a steel pipe as a sample, and the entire pipe was kept at 90 ° C. for 9 days. The amount of metal was determined by a flameless atomic absorption spectrophotometer (Perkin Elmer 5100). The test results are shown in the right column of [Table 1]. In Table 1, the total metal elution amount indicates the relative elution amount when the elution amount of the sample (No. 20) which was not subjected to the ozone oxidation treatment after the electrolytic combined polishing was set to 1.

[0022]

[Table 1]

As is clear from the results in Table 1, the sample No. satisfying all the requirements specified in the present invention. Entire metal elution amount of from 1 to 9 shall remain buffing (Sample No.15)
And it is easily understood that it shows excellent elution resistance, which is １ ／ or less as compared with that of the electrolytic composite polishing as it is (sample No. 20).

On the other hand, in Comparative Example No. 11, the heating oxidation treatment conditions were within the range specified in the present invention. However, although the elution resistance in ultrapure water was excellent, the surface roughness before heating was slightly rough. Due to poor smoothness and relatively large surface area, the effect is not sufficiently exhibited as compared with the examples of the present invention.

In Nos. 12 and 17, oxidation by ozone did not proceed because the temperature of the heat oxidation treatment was low, and an oxide film sufficient to obtain corrosion resistance in ultrapure water was not formed, so that no effect of the heat oxidation treatment was observed. .

In Nos. 13 and 18, the effect of heat oxidation treatment can be seen due to the high temperature, but the same effect can be obtained even without the addition of ozone, which departs from the gist of the present invention (low temperature oxidation treatment). .

In Nos. 14 and 19, since the ozone content in the heating and oxidizing atmosphere was insufficient, the formation of a dense oxide film was insufficient and the effect of improving the corrosion resistance was small. In No.16, the heating oxidation temperature was sufficient, but the oxidation treatment time was insufficient. In the case of stainless steel having poor heat conductivity, a non-uniform oxide film, which is considered to be due to local temperature unevenness, was formed, and the effect of improving corrosion resistance was insufficient. (B) Gas emission comparison test Insert the oxidized test piece (width 25 mm, length 50 mm, plate thickness 2 mm) into an ultra-high vacuum gas emission test device with an internal volume of 3 liters, and reduce the entire device to 10 ^-10 Torr or less. After exhausting
The test piece was heated to 200 ° C. at a heating rate of 10 ° C./min. The pressure of the released gas was measured with an automatic range ultrahigh vacuum gauge (MIG-920), and the gas component was measured using a quadrupole gas mass spectrometer (AQA-100MPX). The test results are shown in the right column of [Table 2]. In Table 2, the amount of gas released at 200 ° C. indicates the relative release amount when the release amount of the sample (No. 6) which was not subjected to the oxidation treatment after electrolytic combined polishing was set to 1. Most of the heat release gas was water.

[0028]

[Table 2]

(C) Elemental analysis of the inner surface of the tube by Auger electron spectroscopy The effect of the oxidizing treatment by the presence or absence of ozone in atmospheric oxygen was investigated for C, Ni, Cr, Fe and O on the polished surface. In the case of a sample whose surface roughness is 0.1 μm (Rmax) by electrolytic combined polishing, the temperature is reduced from 150 ° C.
Surface enrichment of r was observed, and impurities (carbon) were also oxidized and removed. On the other hand, in the case of oxygen alone, a peak of Cr appeared from 250 ° C., and a peak of carbon remained even at 250 ° C. 200 ° C
Fig. 1 shows the results of elemental analysis in the depth direction of the sample oxidized for 2 hours.
Shown in FIG. 1A shows a case where ozone (O ₃ ) is added, and FIG. 1B shows a case where only oxygen is added. The horizontal axis of each graph in FIG. 1 indicates the sputtering time, that is, the depth from the surface, and the vertical axis indicates the relative concentration. In addition to the concentration of Cr on the outermost surface,
It can be clearly seen that the ozone-added one has a thicker oxide film and a higher oxygen concentration in the film than the oxygen-only one, and a dense oxide film is formed. It is considered that the effect of reducing gas release and ion elution of the present invention is due to the increase in the thickness and density of the oxide film.

[0030]

According to the surface treatment method for a stainless steel member of the present invention, the surface is polished so as to have a surface roughness of 1 μm or less, and the oxide film is formed in a dry oxygen atmosphere containing ozone. In this manner, the oxide film formed on the surface of the member becomes dense, and the elution amount of the impurity from the surface of the member can be extremely reduced, in combination with the action of oxidizing and removing impurities contained in ozone.

Therefore, by using a stainless steel member which has been subjected to surface treatment by this method, the amount of outgassing and the amount of ion elution can be greatly reduced, so that not only ultra-high vacuum equipment and high-purity gas piping but also electronic equipment It is expected to make a significant contribution to ultrapure water production equipment such as production, bio / pharmaceutical raw material production, and chlorofluorocarbon alternative cleaning.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of elemental analysis in the depth direction when a sample surface is oxidized.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-274254 (JP, A) JP-A-64-31956 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 8 / 14,8 / 02

Claims (1)

(57) [Claims] 1. A stainless steel member polished so as to have a surface roughness of 1 μm or less has an ozone content of 0.5 to 10 μm.
150 to 300% in a dry oxygen atmosphere at volume%
A surface treatment of a stainless steel member characterized by forming an oxide film on the surface of the stainless steel member by performing a heating oxidation treatment at a temperature of more than 1 hour to 10 hours at a temperature of ℃. Method.